Electric protective device



Aug. 25, 1942. R. w. PRICE ELECTRIC PROTECTIVE DEVICE FilGd July 13,1939 1 'II'III "I,

WITNESSES:

INVENTOR Robert WPrice.

Patented Aug. 25, 1942 azsassc suzc'rmo PROTECTIVE names Robert W.Price, Wilkinsburg, Pa., assignor to Westinghouse Electric 3;Manufacturing Company, East Pittsburgh, 2a., a corporation ofPennsylvania Application-July is, 1939, Serial No. earns (Cl. zoo-12s)12 Claims.

My invention relates to electrical protective devices, and especially tothat type which is designed to protect electric circuits as well asapparatus served thereby from damage arising from rela tively smalloverloads which may become harmful because of their continued duration,as well as from relatively heavy overloads or short circuits, but willnot operate to open the circuit on harmless overloads, such as overloadsof a magnitude or duration so small that no injury could resulttherefrom.

The proper protection of electrical appliances, such as small motors andlighting circuits, depends upon the selection of a fuse which willdistinguish between harmless and harmful overloads. The standardcommercial fuse does not possess sufficient time lag to provideprotection on light continuing overloads, and at the same time notoperate to open the circuit upon energizing the apparatus protected ifit draws appreciable starting current. Thus such a fuse is either blownby the starting current drawn, or the apparatus lacks protection onlight overloads which can become dangerous due to their continuedduration.

For example, assume a small motor draws a full load current of 5 amperesand that its starting current is approximately 800% of full loadcurrent. It is obvious that a standard 5 ampere fuse would blow everytime the motor is started. 0n the other hand, if a higher rated fusesuch as a ampere fuse is used to protect the motor, it would not beprotected on overloads of 100% which could seriously damage the motor ifprolonged for any length of time.

The fuse to be described is designed to operate in 7 seconds onoverloads of 650%, 29 seconds on overloads of 250% and in approximately2700 seconds on overloads of 25%.

Thermal overload devices having an operating time lag greater than thatof the ordinary type of fuse have been used heretofore, but in order toobtain protection from relatively great overloads and short circuits, ithas been necessary in the past to provide a separate fuse connected inseries with such devices It is, therefore, an object of my invention toprovide in a single protective device the combined characteristics of afuse and a time lag cutout.

A further object of my invention is to provide an electric protectivedevice having relatively few essential parts, which maybe simply andeconomically constructed.

Another object of my invention is to provide an designed to giveprotection against heavy overloads and short circuits, which element isalso designed to heat a fusible electric bond to give a time lagprotection for relatively smaller continuing overloads.

Another object of my invention is to provide an electric protectivedevice having a plurality of fusible portions to give protection fordifferent harmful load conditions, which device has a single means forinterrupting the circuit through the device, upon operation of any ofthe fusible por tions.

These and other objects of my invention will become more apparent uponconsideration of the following specification and the annexed drawing inwhich:

Figure l is a central vertical sectional view of my device;

Fig. 2 is a view similar to Fig. 1 showing the circuit through the fuseinterrupted at the fusible alloy juncture;

Fig. 3 is a transverse section taken on the line III-III of Fig. 1; and

Fig. 4 is a view similar to Fig. 1 showing the circuit through the fuseinterrupted at the fusible portion of the heating element.

My protective device consists of a pair of opposed cup-shaped insulatingmembers 2, 4. One of the members 4 is provided with an outwardlyprojecting flange 8 and a reduced tubular extension 9 having a flattenedouter side portion 7.

The other insulating member 2 telescopes over the reduced tubularsection 9 and abuts against flange 8. The insulating member 2 has aninner flattened side portion 5 to engage the flat portion 1 on theinsulating member 4 to prevent relative rotation of the insulatingmembers when the fuse is assembled. These members are formed of anydesired insulating material, the outer member 2 being preferably formedof glass or other transparent material so that a visual indication ofthe condition of the fuse will be afforded. The insulating members aresecured together by a side contact sleeve 6 having an inwardlyprojecting flange I0 engaging under the flange 8 on the insulatingmember 4 and threadedly engaging the insulating member 2. The insulatingmember 4 is provided at its bottom with an opening for receiving acenter contact I2 of suitable conducting material which is secured inplace in the opening in any suitable manner. As shown, the contact I2has a flange l4 seated against the outer side of the insulating member 4electric protective device having a fuse element and has outwardly bentportions It at the inner side of the insulating member 4 to secure thesame in position.

A heating coil 20 of any suitable resistance material, such for example,as Nichrome, has one end thereof roughened and secured to the centercontact l2 by any suitable means, such as for example, a mass of solderl8. The heating coil extends into an elongated heater cap 24, having acentral bore 25 in which the heater coil is received. At the end of thebore in the heater cap, there is provided an eccentric aperture throughthe end of the cap for receiving the other end 26 of the heater coil 20.The end 28 of the heater coil is fixedly secured to the cap in anysuitable manner such as, for example, by mechanically pinching the capin the region of the part 26. At the open end of the bore and the heatercap, the heater element 20 is provided with a fusible portion 22 ofreduced cross-section and formed, for example, by providing a nick inthe heater element. A mass of fusible material 28, preferably anysuitable alloy or eutectic metal having a low melting point, such forexample, as

I a low melting point solder, is supported at the top of the heater capand serves to anchor a resilient conductor 30, such as beryllium copper,to the heater cap. The conductor 30 is of such size and shape as tolimit conduction of heat away from the heater cap. The conductor 30 isheld under stress by the mass of fusible material and upon softening ormelting of the fusible material 28, the resilient conductor 30 will moveaway from the heater cap to the position shown in Fig. 2. The resilientconductor 30 is secured between the insulating parts 2 and 4 as at 32when they are assembled and has an end 34 extending into engagement withthe side contact member 6. The heater cap is preferably formed ofsuitable metallic material and may, if desired, have an insulatingcoating for its bored part 25, such as an insulating lacquer, paint orthe like. Inasmuch as the end 26 of the heater coil is connected to theheater cap 24, it need not extend to the fusible material as shown, butmay terminate short of the'same. These features, however, do not alterthe cooperation of the parts or their functions, as hereinafterdescribed.

In the operation of my device, when the current through the deviceattains a certain value, which exists for a predetermined time, theheater develops suflicient heat to gradually raise the temperature ofthe mass of metal on the heater cap to the melting temperature of thefusible alloy, causing the latter to soften and release its hold on thespring, whereupon the spring separates from the heater cap andinterrupts the circuit, as shown in Fig. 2. On heavy overloads and shortcircuits, the heater burns through at its fusible portion 22 beforesumcient heat has been developed to raise the temperature of the heatercap and melt the fusible alloy. The resilient conductor 30 also operatesto interrupt the circuit upon fusing of the fusible portion 22 of theheater element, as shown in Fig. 4, thus giving a wide gap to open thecircuit both on small overloads and heavy short circuits. Thus it can beseen that this device has two distinct points of operation; the point atwhich operation takes place depend ng upon load conditions of thecircuit in which the fuse is placed. On prolonged light overloads, thecircuit is opened at the fusible alloy juncture. On heavy overloads andshort circuits, the heater burns through almost irmnediately. In eachcase the resilient conductor 30 operates to interrupt the circuit. Dueto the fact that light overloads will not burn through the fusibleportion 22 of the heating coil and that the operation of the deviceunder such overloads is dependent on the time necessary for the heaterto heat the heater cap sufllciently to soften or melt the fusible alloy,it is apparent that upon such light prolonged overloads, this devicewill have a much greater time lag than the ordinary fuse of the samerating. However, on heavy overloads or short circuits the fuse operatesimmediately before suflicient heat can be developed to soften or meltthe fusible alloy 28, thus providing a maximum of protection on bothtypes of overloads.

It ,wm be noted that this circuit interrupting device is constructed tobe inserted in standard threaded type fuse h'olders.

It can be further seen that I have provided a circuit interruptingdevice giving protection on short circuits and heavy overloads as wellas on relatively small but prolonged overloads having relatively fewoperating parts and being of relatively simple, and economicalconstruction.

While in accordance with the patent statutes, I have described in detailone embodiment of my invention, it will be obvious to those skilled inthe art that many changes may be made therein, such as omission ofparts, substitution of elements, and other changes apparent to oneskilled in the art, and I do not wish to be limited to the particularembodiment disclosed, except as set forth in the appended claims.

I claim as my invention:

1. In a protective device for electric circuits having a pair ofcontacts, electric heating means connected to one of said contacts, aconducting casing about the heating means and connected thereto, amovable conductor connected to the other of said contacts, and a mass offusible material connecting said casing and conductor whereby saidconductor is movable to interrupt the circuit through the device uponmelting of the fusible material.

2. In a protective device for electric circuits, a casing member havingan open end and a closed end, a heating member extending into the casingthrough said open end and having its inner end connected to the closedend of said casing member, a mass of fusible material supported on saidcasing and. electrically connected to at least one of said members, ang.a movable conductor secured in said fusible material, whereby thecircuit through the device may be interrupted upon melting of saidfusible material.

3. In a protective device for-electric circuits, a casing member havingan open end, a heating member extending into the casing through saidopen end, a mass of fusible material supported on said casing andelectrically connected to at least one of said members, a movableconductor secured in said fusible material, whereby the circuit throughthe device may be interrupted by fusing of the fusible material uponpassage through the device of a current of predetermined magnitude, saidheating member having a portion substantially at the open end of thecasing member adapted to be fused upon passage of a current through thedevice of a predetermined greater magnitude.

4. In a protective device for electric circuits, a casing member havingan open end, a heating member extending into the casing through saidopen end, a mass of fusible material supported on said casing andelectrically connected to at least one of said members, and a resilientconductor secured in said fusible material and biased away therefromwhereby the circuit through the device is interrupted by said resilientconductor when the fusible material melts due to passage through thedevice of a current of a predetermined magnitude, said heating memberhaving a portion substantially at the open end of the casing memberadapted to be fused upon passage therethrough of a current of apredetermined greater magnitude, whereupon the resilient conductor willseparate the fused portions of said heating member.

5. In a protective device for electric circuits having a pair ofcontacts, a mass of fusible material, a stressed resilient contactmember secured therein and a heater member for the fusible material allconnected between said contacts, one of said members having a fusibleportion adapted to fuse upon the passage therethrough of a current of agreater predetermined magnitude than that required to heat said fusiblematerial to its fusing point, whereby said resilient conductor willinterrupt the circuit through the device upon fusing of said fusiblematerial or of said fusible portion.

6. In a protective device for electric circuits having a pair ofcontacts, fuse means connecting said contacts including fusible materialand a heating means therefor, a heat conducting member including ahollow portion for receiving said heating means and a relatively massiveportion between said heating means and fusible material, whereby uponthe passage of a current of a predetermined small magnitude through thedevice, the fusible material will be softened or melted by heatconducted from the heater to interrupt the circuit through the fuse, andthe heater being provided with a portion adapted to fuse upon thepassage through the device of a current of a predetermined largermagnitude.

able terminal, said conducting means including a hollow portion forreceiving a heating means electrically connected thereto, and arelatively massive portion located between said hollow portion and saidfusible material.

9. In a protective device for electric circuits, a casing member havingan open end and a closed end, a heating member extending into the casingthrough said open end and having its inner end connected to the closedend of said casing member, a mass of fusible material supported on saidcasing and a stressed resilient conductor anchored in saidfusible-material, whereby the circuit through the device may beinterrupted upon melting of said fusible material by said resilientconductor.

10. In a 'protective device for electric circuits, a casing memberhaving an open end and a closed end, a heating member extending into thecasing through said open end and having its inner end connected to theclosed end of said cas n member, a mass of fusible material supported onsaid casing, a stressed resilient conductor anchored in said fusiblematerial, and said heating member having a portion adapted 'to be fusedupon the passage of current therethrough of a value greater than thatrequired to fuse said fusible material, whereby the circuit through thedevice may be-interrupted upon melting of said fusible material orfusion of said portion of said heating member, by said resilientconductor.

11. In a protective device, a casing, electric ing different fusingcharacteristics located, respectively, adjacent opposite ends of saidcasing and serially connected with said heating means, and one of saidfusible means being arranged in heat-conducting relation with respect tosaid casing.

12. In a protective device, a casing, electric heating means in saidcasing, fusible means having different fusing characteristics located,respectively,-adjacent opposite ends of said casing and seriallyconnected with said heating means, one of said fusible means beingarranged in heatconducting relation with respect to said casing, andresilient means associated with one of said fusible means to causeseparation of the unfused terminals of either of said fusible means uponfusion thereof.

ROBERT W. PRICE.

